The present invention relates to breakaway steel posts for use with a highway guardrail end terminal system or a crash attenuation system. More particularly, the invention relates to a supplemental energy-absorbing mechanism affixed to such steel posts.
Existing highway guardrail end treatment systems include: the breakaway cable terminal (BCT), the eccentric loader terminal (ELT), the modified eccentric loader terminal (MELT), the vehicle attenuating terminal (VAT), the extruder terminal (ET), the slotted rail terminal (SRT), the sequential kinking terminal (SKT), and the flared energy absorbing terminal (FLEAT).
In all of these systems, breakaway wooden posts, either inserted in foundation tubes (known as BCT breakaway post) or directly installed in the ground (known as controlled release terminal CRT post), are used to facilitate proper breaking of the posts to minimize the potential for snagging on the posts and excessive decelerations on the vehicles in end-on impacts with the terminals. Holes are drilled into the wooden post at and/or below ground level to reduce the cross-sectional area of the post, thus reducing the force required to break the post. Steel breakaway posts based on the slip-base concept have also been developed, but did not receive widespread acceptance due to maintenance problems and higher initial costs.
However, there are situations in which a transportation agency may choose not to use wooden posts for environmental concerns or as a matter of policy. In such situations, breakaway steel post would be an alternative. A prior patent of the inventors relates to various conceptual designs for breakaway posts suitable for use with highway guardrail and end terminal systems. These designs have a predictable breakaway force threshold when impacted along the weak axis (in the direction of end-on impacts with the terminal system) while maintaining a sufficiently high bending force in the strong axis (perpendicular to the weak axis in the direction of side impacts) to provide the required lateral stiffness to the terminal system for side impacts.
The present invention relates to an improved steel post for use with a highway post-and-beam type guardrail at locations where deflection of the post in the soil is limited or not allowed, e.g., posts embedded in concrete or asphalt in such applications as mow strips.
Existing standard guardrail line posts, either wood or steel, require some deflection in the soil to function properly. When a guardrail is impacted, the posts in the immediate vicinity of the impact would typically deflect and absorb some of the impact energy. Deflection of the posts would allow the rail to go into tension and act like a ribbon to contain and redirect the vehicle. If deflection of the posts in the soil is not allowed or limited in such applications as mow strips where the posts are embedded in concrete or asphalt, wooden posts would fracture and steel posts would bend or twist at the base.
The present invention relates to various conceptual designs for energy-absorbing breakaway steel guardrail posts suitable for use at locations where deflection of the post in the soil is limited or not allowed. These designs provide a predictable failure or yielding force threshold when impacted to maintain the required lateral stiffness; a mechanism for adequate energy dissipation by the post; and a limit beyond which the lateral resistance of the post is eliminated.